Does anybody knows how it's done?
I give them stars and crown

Write both vectors in component form:

A = (12.0 u) (cos(30°) i + sin(30°) j ) ≈ (10.4 i + 6.00 j ) u

B = (8.00 u) (cos(80°) i + sin(80°) j ) ≈ (1.39 i + 7.88 j ) u

Subtract B from A :

A - B ≈ (9.00 i - 1.88 j )

(a) The magnitude of this vector is

||A - B|| ≈ √(9.00² + (-1.88 )²) u ≈ 9.20 u

(b) This vector has direction θ such that

tan(θ) ≈ (-1.88 u)/(9.00 u) ≈ -0.209

A - B has a positive x-component and a negative y-component, which means it's directed into the fourth quadrant, so

θ ≈ arctan(-0.209) ≈ -11.8°

(c) The negative sign in the angle found in part (b) indicates that A - B makes an angle of 11.8° below the positive x-axis.

given data:

determine the horse power (h.p) = ?

force applied to move the box(f) = 10 pounds,

box lifted from a distance         (d) = 3 feet

time taken to lift                         (t) = 10 sec,

the horse power is defined as amount of work required to move a load. the horse power is equal to 550 foot-pound per second

                  1 h.p   = 550 foot-pound/second

it can also be defined as the the load that need to be move a body for certain distance in a certain amount of time.

mathematically,

                      h.p = (force × distance)/ time

                            = (10 × 3)/ 10

                            = 30/10

                            = 3 foot -pound/sec

hence, the horse power is needed to move the box is 3 foot-pound/second

important note: 1 h.p = 550 foot-pound/second = 746 watts